Preheat oven to 350 degrees.
Saute Mushrooms, onions and bell peppers in butter.
Meanwhile, mix soups, milk and cheese in saucepan.
Add sautéed mix into the soup mix.
Heat until cheese is melted, but be careful not to burn.
In casserole dish, mix spaghetti with chicken.
Pour the soup mixture over spaghetti and chicken. Mix together.
Slice Velveeta cheese on top of dish.
Bake at 350 degrees until the cheese is melted.